1. Field of the Invention
The present invention relates to a screen assembly and a rear-projection type graphic display device both of which can block overscanned light that is produced in a peripheral area of image light when back-projecting it emitted from a projection area on a screen having an optical transparency
2. Description of the Related Art
In the projection type graphic display device that projects an image displayed on a liquid crystal panel (i.e. a type of image display element or light modulation device) on a screen in enlargement due to a projection optical system, there are a variety of structural forms. They are broadly-divided into a group of front-projection type graphic display devices for projecting images on the screen from the front and another group of rear-projection type graphic display devices for projecting images on the screen from behind. In view of widespread utilization, the rear-projection type graphic display device is popular in comparison with the front-projection type graphic display device since the former is compact so as to require a smaller installation area.
As for the operation of projecting an image projected from a projection unit on a rear (back) surface of the screen, in the above rear-projection type graphic display device, it is difficult for the projection unit to project an image so that a projected image conforms with a screen size (or overall size) perfectly. Thus, in order to prevent a projected image from getting insufficiency at the periphery of the screen, there has been performed so-called “overscan” to project an image in a somewhat larger size than the screen size (overall size). In this overscan operation, a light projected toward an external side of the screen size is often called to as “overscanned light”.
Japanese Patent Publication Laid-open No. 11-133509 discloses a fresnel lens sheet and a rear-projection type display device. In this display device, a screen comprises a transparent panel, a lenticular lens sheet and a fresnel lens sheet, which are overlapped in this order. On the side of the transparent panel of the screen, there is an opaque screen frame forming a window frame smaller than the fresnel lens sheet in order to project an image from the back surface of the fresnel lens sheet. In the display device constructed above, the overscanned light projected against the outer circumference of the back surface of the fresnel lens sheet is blocked by the opaque screen frame outside the window frame. Further, in order to prevent an occurrence of stray light, which might be produced since the overscanned light projected to the outer periphery of the back surface of the fresnel lens sheet is reflected by the fresnel lens sheet, a flat area is formed along the outer periphery of the back surface of the fresnel lens sheet.